Wavelength cross-connect

ABSTRACT

A wavelength cross connect is provided in which wavelength channels are individually switchable from one of a first set of ports to one of a second set of ports. Add and drop capability is provided on the sets of ports. Some embodiments feature a single row of ports, while others feature two dimensional arrays of ports. Some embodiments employ one dispersive element per port, and others employ one dispersive element per row of ports. Embodiments featuring transmissive and non-transmissive switching elements are provided.

FIELD OF THE INVENTION

This invention relates to the field of DWDM fibre opticstelecommunications and in particular to the field of all-opticalswitching.

BACKGROUND OF THE INVENTION

The advent of DWDM fibre optics telecommunications systems in the early1990s have enabled a dramatic increase in the transmission capacity overpoint-to-point links. This was achieved through multiplexing of a largenumber of individually modulated light beams of different wavelengthsonto the same optical fibre. Typical systems installed today would have64 or more independent channels precisely aligned onto an ITU-Tstandardized grid at 100 GHz, 50 GHz or even narrower channel spacing.With routine modulation speeds of 10 Gb/s and attaining 40 Gb/s inlaboratory experiments, it is not unusual to obtain aggregatedcapacities in the order of several terabits per second of informationbeing transmitted onto a single optical fibre (S. Bigo, Optical FibreCommunications conference, WX 3, pp. 362-364, Anaheim, 2002). At thesame time, electrical switching capacities have been growing at a muchslower rate, with current largest electrical switch matrices limited totypically 640 Gb/s in a single stage. Furthermore, the cost ofconverting the signal from optical to electrical for switching and thenback from electrical to optical becomes prohibitively expensive as thenumber of optical channel increases. All optical switching technologiesare therefore becoming more and more attractive to manage the enormousbandwidth being transmitted over optical fibres.

A typical all-optical switch would consist of a large core all-opticalswitch matrix surrounded by DWDM demultiplexers and multiplexers at eachfibre interface. However, for large number of wavelengths channels peroptical fibre, this leads to a very large switching core size: forexample, a 50 GHz channel spacing system with 128 channels per fibrewould require a 1024×1024 switching matrix to switch traffic between 8incoming fibres to 8 outgoing fibres on a per wavelength basis. Largeoptical switching matrices are hard to fabricate, complex to control,require overwhelming fibre management and are very expensive.Furthermore, in the absence of wavelength conversion, only a sub-set ofthe switching matrix capacity is actually in use: each wavelength beingswitched independently, only 128 8×8 independent connections are used inthe 1024×1024 available (0.8% of the overall switching capacity). Thishuge inefficiency is the primary reason for considering a wavelengthswitching architecture in which the DWDM demultiplexing and multiplexingare integrated with the switching function.

An example of a wavelength selective all-optical switch is called awavelength selective cross-connect WSXC (R. E. Wagner, Journal ofLightwave Technology, Vol. 14, No. 6, June 1996, also U.S. Pat. No.6,097,859) by Solgaard et al. Such a device generally has N incomingfibres and N outgoing fibres, each fibre being capable of transporting Mwavelength channels. The WXC enables independent switching of each ofthe M wavelength channels from the N incoming fibres to the N outgoingfibres. It is functionally equivalent to an input array of N wavelengthdemultiplexers routed to an output array of N wavelength multiplexersthrough an array of M N×N optical switches. In such a WXC, there areM×N×N possible optical paths, which is exactly the required flexibilityin the absence of wavelength conversion. For example, in the casementioned above of a 128 channel system at 50 GHz spacing with 8 fibresin and 8 fibres out, the standard large optical core based switch wouldhave over a million possible connections, whereas only 8192 are needed,which is exactly what the WXC architecture enables (128×8×8).

SUMMARY OF THE INVENTION

According to one broad aspect, the invention provides a wavelength crossconnect comprising: a first plurality of lenses stacked vertically; asecond plurality of lenses stacked vertically, spaced from said firstplurality of lenses, non-overlapping in vertical space with said firstplurality of lenses; a first plurality of dispersive elements, with onedispersive element substantially in a first focal plane of each of saidfirst plurality of lenses; a second plurality of dispersive elements,with one dispersive element substantially in a second focal plane ofeach of said second plurality of lenses; a first array of switchingelements controllable in two directions, the first array beingsubstantially in a second focal plane of each of said first plurality oflenses; a second array of switching elements controllable in twodirections, the second array being substantially in a first focal planeof each of said second plurality of lenses; in a first plurality ofoptical ports a respective optical port positioned to input lightonto/receive light from each of said first plurality of lenses; in asecond plurality of optical ports a respective optical port positionedto input light onto/receive light from each of said second plurality oflenses; wherein light entering any of said first plurality of opticalports or said second plurality of ports is switchable to any of thefirst plurality of optical ports and any of said second plurality ofoptical ports.

In some embodiments, the switching elements are MEMS switching elements.

In some embodiments, each first bulk optical element is selected from agroup consisting of a lens or a curved mirror.

In some embodiments, the dispersive element is selected from a groupconsisting of: a diffraction grating, either reflection and transmissiontype, prisms.

According to another broad aspect, the invention provides a wavelengthcross connect comprising: a first plurality of lenses stackedvertically; a second plurality of lenses stacked vertically, spaced fromsaid first plurality of lenses, non-overlapping in vertical space withsaid first plurality of lenses; a first dispersive element at least partof which is substantially in a first focal plane of each of said firstplurality of lenses; a second dispersive element at least part of whichis substantially in a second focal plane of each of said secondplurality of lenses; a first array of switching elements controllable intwo directions, the first array being substantially in a second focalplane of each of said first plurality of lenses; a second array ofswitching elements controllable in two directions, the second arraybeing substantially in a first focal plane of each of said secondplurality of lenses; in a first plurality of optical ports a respectiveoptical port positioned to input light onto/receive light from each ofsaid first plurality of lenses; in a second plurality of optical ports arespective optical port positioned to input light onto/receive lightfrom each of said second plurality of lenses; wherein light entering anyof said first plurality of optical ports or said second plurality ofports is switchable to any of the first plurality of optical ports andany of said second plurality of optical ports.

In some embodiments, the switching elements are MEMS switching elements.

In some embodiments, each first bulk optical element is selected from agroup consisting of a lens or a curved mirror.

In some embodiments, the dispersive element is selected from a groupconsisting of: a diffraction grating, either reflection and transmissiontype, prisms.

According to another broad aspect, the invention provides a wavelengthcross connect comprising: a first plurality of lenses stackedvertically; a second plurality of lenses stacked vertically, spaced fromsaid first plurality of lenses, non-overlapping in vertical space withsaid first plurality of lenses; a first plurality of dispersiveelements, with one dispersive element substantially in a first focalplane of each of said first plurality of lenses; a second plurality ofdispersive elements, with one dispersive element substantially in asecond focal plane of each of said second plurality of lenses; a firstarray of transmissive switching elements controllable in two directions,the first array being substantially in a second focal plane of each ofsaid first plurality of lenses; a second array of transmissive switchingelements controllable in two directions, the second array beingsubstantially in a first focal plane of each of said second plurality oflenses; in a first plurality of optical ports a respective optical portpositioned to input light onto/receive light from each of said firstplurality of lenses; in a second plurality of optical ports a respectiveoptical port positioned to input light onto/receive light from each ofsaid second plurality of lenses; wherein light entering any of saidfirst plurality of optical ports or said second plurality of ports isswitchable to any of the first plurality of optical ports and any ofsaid second plurality of optical ports.

In some embodiments, the transmissive switching elements are one of aliquid crystal beam steering element, an acousto-optic beam deflector,part of a solid state phase array, a controllable hologram, and aperiodically poled Lithium Niobate beam deflector.

In some embodiments, each first bulk optical element is selected from agroup consisting of a lens or a curved mirror.

In some embodiments the dispersive element is selected from a groupconsisting of: a diffraction grating, either reflection and transmissiontype, prisms.

According to another broad aspect, the invention provides a wavelengthcross connect comprising: a first plurality of lenses stackedvertically; a second plurality of lenses stacked vertically, spaced fromsaid first plurality of lenses, non-overlapping in vertical space withsaid first plurality of lenses; a first plurality of dispersiveelements, with one dispersive element substantially in a first focalplane of each of said first plurality of lenses; a second plurality ofdispersive elements, with one dispersive element substantially in asecond focal plane of each of said second plurality of lenses; a firstarray of switching elements controllable in two directions, the firstarray being substantially in a second focal plane of each of said firstplurality of lenses; a second array of switching elements controllablein two directions, the second array being substantially in a first focalplane of each of said second plurality of lenses; a first twodimensional array of optical ports; a second two dimensional array ofoptical ports; for each row of said first two dimensional array ofoptical ports, a respective first bulk optical element having opticalpower and having a fourth focal plane substantially coplanar with saidfirst focal plane of said second plurality of lenses; for each row ofsaid second two dimensional array of optical ports, a respective secondbulk optical element having optical power and having a fifth focal planesubstantially coplanar with said second focal plane of said firstplurality of lenses; wherein each wavelength channel of a WDM signalentering at a port of said first array of optical ports is individuallyswitchable to any of the port in first array of optical ports in a samerow as the port where the WDM signal entered and any of the second arrayof optical ports through appropriate control of the array of switchingelements.

In some embodiments, the switching elements are MEMS switching elements.

In some embodiments, each bulk optical element is a lens or a curvedmirror.

In some embodiments, the dispersive element is selected from a groupcomprising: a diffraction grating, either reflection and transmissiontype, prisms.

According to another broad aspect, the invention provides a wavelengthcross connect comprising: a first plurality of lenses stackedvertically; a second plurality of lenses stacked vertically, spaced fromsaid first plurality of lenses, non-overlapping in vertical space withsaid first plurality of lenses; a first plurality of dispersiveelements, with one dispersive element substantially in a first focalplane of each of said first plurality of lenses; a second plurality ofdispersive elements, with one dispersive element substantially in asecond focal plane of each of said second plurality of lenses; a firstarray of switching elements controllable in two directions, the firstarray being substantially in a second focal plane of each of said firstplurality of lenses; a second array of switching elements controllablein two directions, the second array being substantially in a first focalplane of each of said second plurality of lenses; a first twodimensional array of optical ports; a second two dimensional array ofoptical ports; a first bulk optical element having optical power andhaving a fourth focal plane substantially coplanar with said first focalplane of said second plurality of lenses; a second optical elementhaving optical power and having a fifth focal plane substantiallycoplanar with said second focal plane of said first plurality of lenses;wherein each wavelength channel of a WDM signal entering at port of saidfirst array of optical ports is individually switchable to any of theport in first array of optical ports in a same row as the port where theWDM signal entered and any of the second array of optical ports throughappropriate control of the array of switching elements.

In some embodiments, the switching elements are MEMS switching elements.

In some embodiments, each bulk optical element is a lens or a curvedmirror.

In some embodiments, the dispersive element is selected from a groupcomprising: a diffraction grating, either reflection and transmissiontype, prisms.

According to another broad aspect, the invention provides an arrangementcomprising: a first two dimensional array of optical ports; a first twodimensional array of waveguide dispersive elements on a plurality ofwaveguide substrates, with one waveguide dispersive element per opticalport in said first two dimensional array of optical ports, the first twodimensional array of waveguide dispersive elements collectively having afirst output plane; for each row of said first two dimensional array ofoptical ports, a respective first bulk optical element having opticalpower and having a first focal plane substantially coplanar with saidfirst output plane, and having a second focal plane; a first array ofswitching elements substantially in the second focal plane, eachswitching element being adapted to switch in both a horizontal andvertical direction; a second two dimensional array of optical ports; asecond two dimensional array of waveguide dispersive elements on aplurality of waveguide substrates, with one waveguide dispersive elementper optical port in said second two dimensional array of optical ports,the second two dimensional array of waveguide dispersive elementscollectively having a second output plane; for each row of said secondtwo dimensional array of optical ports, a respective second bulk opticalelement having optical power and having a fifth focal plane and having asixth focal plane substantially coplanar with the second output plane; asecond array of switching elements substantially in the fifth focalplane, each switching element being adapted to switch in both ahorizontal and vertical direction; wherein each wavelength channel of aWDM signal entering at one of said first array of optical ports isindividually switchable to any of the optical ports of the first arrayin a same row as the port through which the signal entered and any ofthe optical ports of the second array through appropriate control of thearray of switching elements.

In some embodiments, the switching elements are MEMS switching elements.

In some embodiments, each bulk optical element having optical power is alens or a curved mirror.

In some embodiments, the dispersive elements comprise arrayed waveguidegratings or Echelle gratings.

According to another broad aspect, the invention provides an arrangementcomprising: a first two dimensional array of optical ports; a first twodimensional array of waveguide dispersive elements on a plurality ofwaveguide substrates, with one waveguide dispersive element per opticalport in said first two dimensional array of optical ports, the first twodimensional array of waveguide dispersive elements collectively having afirst output plane; a first bulk optical element having optical powerand having a first focal plane substantially coplanar with said firstoutput plane, and having a second focal plane; a first array ofswitching elements substantially in the second focal plane, eachswitching element being adapted to switch in both a horizontal andvertical direction; a second two dimensional array of optical ports; asecond two dimensional array of waveguide dispersive elements on aplurality of waveguide substrates, with one waveguide dispersive elementper optical port in said second two dimensional array of optical ports,the second two dimensional array of waveguide dispersive elementscollectively having a second output plane; a second bulk optical elementhaving optical power and having a fifth focal plane and having a sixthfocal plane substantially coplanar with the second output plane; asecond array of switching elements substantially in the fifth focalplane, each switching element being adapted to switch in both ahorizontal and vertical direction; wherein each wavelength channel of aWDM signal entering at one of said first array of optical ports isindividually switchable to any of the optical ports of the first arrayin a same row as the port through which the signal entered and any ofthe optical ports of the second array through appropriate control of thearray of switching elements.

In some embodiments, the switching elements are MEMS switching elements.

In some embodiments, each bulk optical element having optical power is alens or a curved mirror.

In some embodiments, the dispersive elements comprise arrayed waveguidegratings or Echelle gratings.

According to another broad aspect, the invention provides a wavelengthcross connect comprising: a first plurality of lenses stackedvertically; a second plurality of lenses stacked vertically, spaced fromsaid first plurality of lenses, non-overlapping in vertical space withsaid first plurality of lenses; a first plurality of dispersiveelements, with one dispersive element substantially in a first focalplane of each of said first plurality of lenses; a second plurality ofdispersive elements, with one dispersive element substantially in asecond focal plane of each of said second plurality of lenses; a firstarray of transmissive switching elements controllable in two directions,the first array being substantially in a second focal plane of each ofsaid first plurality of lenses; a second array of transmissive switchingelements controllable in two directions, the second array beingsubstantially in a first focal plane of each of said second plurality oflenses; a first two dimensional array of optical ports; a second twodimensional array of optical ports; for each row of said first twodimensional array of optical ports, a respective first bulk opticalelement having optical power and having a fourth focal planesubstantially coplanar with said first focal plane of said secondplurality of lenses; for each row of said second two dimensional arrayof optical ports, a respective second bulk optical element havingoptical power and having a fifth focal plane substantially coplanar withsaid second focal plane of said first plurality of lenses; wherein eachwavelength channel of a WDM signal entering at port of said first arrayof optical ports is individually switchable to any of the port in firstarray of optical ports in a same row as the port where the WDM signalentered and any of the second array of optical ports through appropriatecontrol of the array of switching elements.

In some embodiments, each bulk optical element a lens or a curvedmirror.

In some embodiments, the dispersive element is selected from a groupcomprising: a diffraction grating, either reflection and transmissiontype, prisms.

According to another broad aspect, the invention provides a wavelengthcross connect comprising: a first plurality of lenses stackedvertically; a second plurality of lenses stacked vertically, spaced fromsaid first plurality of lenses, non-overlapping in vertical space withsaid first plurality of lenses; a first plurality of dispersiveelements, with one dispersive element substantially in a first focalplane of each of said first plurality of lenses; a second plurality ofdispersive elements, with one dispersive element substantially in asecond focal plane of each of said second plurality of lenses; a firstarray of transmissive switching elements controllable in two directions,the first array being substantially in a second focal plane of each ofsaid first plurality of lenses; a second array of transmissive switchingelements controllable in two directions, the second array beingsubstantially in a first focal plane of each of said second plurality oflenses; a first two dimensional array of optical ports; a second twodimensional array of optical ports; a first bulk optical element havingoptical power and having a fourth focal plane substantially coplanarwith said first focal plane of said second plurality of lenses; a secondoptical element having optical power and having a fifth focal planesubstantially coplanar with said second focal plane of said firstplurality of lenses; wherein each wavelength channel of a WDM signalentering at port of said first array of optical ports is individuallyswitchable to any of the port in first array of optical ports in a samerow as the port where the WDM signal entered and any of the second arrayof optical ports through appropriate control of the array of switchingelements.

In some embodiments, each bulk optical element a lens or a curvedmirror.

In some embodiments, the dispersive element is selected from a groupcomprising: a diffraction grating, either reflection and transmissiontype, prisms.

According to another broad aspect, the invention provides an arrangementcomprising: a first plurality of lenses stacked vertically; a secondplurality of lenses stacked vertically, spaced from said first pluralityof lenses, non-overlapping in vertical space with said first pluralityof lenses; a first plurality of dispersive elements, with one dispersiveelement substantially in a first focal plane of each of said firstplurality of lenses; a second plurality of dispersive elements, with onedispersive element substantially in a second focal plane of each of saidsecond plurality of lenses; a first array of switching elementscontrollable in two directions, the first array being substantially in asecond focal plane of each of said first plurality of lenses; a secondarray of switching elements controllabe in two directions, the secondarray being substantially in a first focal plane of each of said secondplurality of lenses; a first plurality of two dimensional arrays ofoptical ports; a second plurality of two dimensional arrays of opticalports; for each two dimensional array of said first plurality of twodimensional arrays of optical ports, a respective first bulk opticalelement having optical power and having a fourth focal planesubstantially coplanar with said first focal plane of said secondplurality of lenses; for each two dimensional array of said secondplurality of two dimensional arrays of optical ports, a respectivesecond bulk optical element having optical power and having a fifthfocal plane substantially coplanar with said second focal plane of saidfirst plurality of lenses; wherein each wavelength channel of a WDMsignal entering at one of said first plurality of arrays of opticalports is individually switchable to any of the first plurality of arraysof optical ports and any of the second plurality of arrays of opticalports through appropriate control of the array of switching elements.

In some embodiments, the switching elements are MEMS switching elements.

In some embodiments, the switching elements are transmissive.

In some embodiments, each bulk optical element is selected from a groupconsisting of a lens, a curved mirror, an assembly of lenses andmirrors, and an assembly of lenses, mirrors and a curved mirror.

In some embodiments, the second bulk optical element is selected from agroup consisting of a lens, a curved mirror, an assembly of lenses andmirrors, and an assembly of lenses, mirrors and a curved mirror.

In some embodiments, the dispersive element is selected from a groupcomprising: a diffraction grating, either reflection and transmissiontype, prisms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows top and side views of a conventional wavelength switchconfigured as a 1×5 wavelength selective switch using free-space opticsand MEMS switching elements;

FIG. 2 shows top and side views of a ROADM with large number of add/dropports configured as a 1×25 wavelength selective switch using free-spaceoptics and MEMS switching elements;

FIG. 3 shows a perspective view of the ROADM of FIG. 2;

FIG. 4 shows top and side views of a ROADM provided with a large numberof add/drop ports configured as a 1×25 wavelength selective switch usingwaveguide optics and MEMS switching elements;

FIG. 5 shows a wavelength cross-connect arrangement using free-spaceoptics and MEMS switching elements, provided by an embodiment of theinvention;

FIG. 6A shows top and side views of a WXC/ROADM device provided by anembodiment of the invention using free-space optics and MEMS switchingelements, in which each optical port has 5 local add/drop ports;

FIG. 6B shows the add/drop/switch function of the device of FIG. 6A;

FIG. 7 shows a perspective view of the elements of the embodiment shownin FIG. 8;

FIG. 8 shows top and side views of a WXC/ROADM device provided by anembodiment of the invention using waveguide optics and MEMS switchingelements, in which each optical port has 5 local add/drop ports;

FIG. 9 shows top and side views of a WXC/ROADM provided by an embodimentof the invention with a large number of add/drop ports device usingfree-space optics and MEMS switching elements, in which each opticalport has 25 local add/drop ports;

FIG. 10 shows top and side views of a WXC/ROADM provided by anembodiment of the invention with a large number of add/drop ports deviceusing waveguide optics and MEMS switching elements, in which eachoptical port has 25 local add/drop ports; and

FIG. 11 shows top and side views of another embodiment of a WXC/ROADMdevice as per the invention using transmissive switching elements andwaveguide optics, in which each optical port has 5 local add/drop ports.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed descriptions of FIGS. 1 to 11 are used to explainthe mode of operation of the invention and describe the preferredembodiments are per the invention, but should not be understood innarrow terms. Some of the elements shown can be replaced by otherrealizations performing similar tasks. For example, wavelengthdispersion can be realized through diffraction gratings (both reflectionand transmission type) or prisms in free-space embodiments or througharrayed waveguide gratings or Echelle gratings in waveguide embodiments.Bulk optical elements having optical powers can be any of a lens, acurved mirror, or any suitable combination of optical elements, eitherspherical or cylindrical, that provide the appropriate optical function.The array of switching means can be either reflective (mirrors, tunablegratings, interferometric arrangements of fixed and movable membranes,etc.), with the best mode being micro-mirror arrays fabricated throughmicro-fabrication processes, or transmissive (liquid crystal,electro-holograms, optical phase arrays, tiltable micro-prisms ormovable micro-lenses, etc.). An example of a liquid crystal based switchis shown in: Patel et al., Photonics Technology Letters, Vol. 7, No. 5,May 1995. Waveguide and free space embodiments are possible to performeach of the dispersion and optical coupling steps, and any arbitraryappropriate combination can be employed. Although most of thedescriptions will explain how to use arrangements as per the inventionas a ROADM with multiple drop ports or ROADM/WXC with multiple dropports, more generalization is possible without departing from the spiritof the invention. For example, since light paths are bidirectional, dropports can also be used as add ports or inputs for outputs. Furthermore,input or add and output or drop ports being essentially equivalent,their choice is arbitrary and should not limit the scope of theinvention. Consistent choices will be made throughout the following forease of description: unless otherwise specified, the middle port in agroup of ports is used as input/output, while the remaining ports in thegroup are used as add/drop ports. However, this is completely arbitrary.

In the following description of all figures except 3D perspective views(FIGS. 3 and 7), the top part of each figure shows a top view, alsoreferred to as the dispersion plane due to the choice of orientation ofthe dispersive elements, while the bottom part of the figure shows theside view.

FIG. 1 shows a known wavelength switch taught in D. M. Marom et al.,Optical Fibre Communications conference, PD FB7, Anaheim, 2002. It isconfigured as a 1×5 with MEMS switching elements.

A group of 5 optical ports 10 is provided in the form of a linear arrayof optical fibres coupled to an array of micro-lenses 12 used tosubstantially collimate/focus the light beams from/to the opticalfibres. In the cited reference, the middle fibre is used as an inputport, while the 4 others are used as outputs, although light paths goingfrom the middle fibre back to the middle fibre are possible when used inconjunction with an optical circulator (thus the denomination as a 1×5arrangement).

In operation, a light beam containing multiple wavelengths is inputthrough the middle optical port, is collimated by the middle micro-lensand is directed to a diffraction grating 14 through a telescopearrangement consisting of a coupling lens 16 and a main lens 18. Afterreflecting from the diffraction grating 14, the light beam isdemultiplexed into a plurality of wavelength channels, each impinging ona corresponding MEMS switch element 20. This MEMS can tilt in the planeof the dispersion to route the wavelength channels to alternatelocations on the diffraction grating 14. The images of these alternatelocations through the telescope can be made to precisely align to one ofthe micro-lens, thus the wavelength channels is made to couple to aselectable optical port.

As is known to a person skilled in the art, off-axis aberrations in anyoptical system worsen dramatically as the field of view is increased.This is all the more true when the optical system is already workingoff-axis, which is the case in the dispersion plane because of thephysical extent of the MEMS array 20. In the cited reference, increasingthe number of optical ports would mean a bigger image for the telescope,and thus a bigger field of view for the main lens in particular.Therefore, the wavelength switch as per the prior art is limited to asmall number of optical ports. Typically, no more than 8 ports can bearranged in such an optical system without generating excessive penaltyin either optical performance (mainly insertion loss uniformity overwavelength) or size.

FIG. 2 shows a wavelength switch providing a large number of opticalports that can be used for example as a ROADM with a large number ofadd/drop ports. In the example shown on FIG. 2, the wavelength switchcan be configured as a 1×25. This is a variant of a system taught inU.S. Pat. No. 6,549,699 to Belser et al.

This dramatic increase in scalability in number of ports is achieved byusing a two dimensional arrangement of optical ports consisting of a twodimensional array of fibres 30 connected to a two dimensional array ofmicro-lenses 32 to substantially collimate/focus light beams as theyemerged/are coupled to the optical fibres and by using an array of MEMSswitching elements 34 capable of directing light beams in both the planeof dispersion and the plane perpendicular to the plane of dispersion. Inthe example shown in FIG. 2, the ports are arranged in a 5×5 array,enabling one input and 25 potential outputs, thus the 1×25 naming(counting the path from the input back to itself as one possible path,although requiring an external circulator).

In operation, a light beam containing multiple wavelengths is inputthrough the middle optical port, is collimated by the middle micro-lensand is directed to the diffraction through a telescope arrangementconsisting of a coupling lens 36 and a main lens 38. After reflectingfrom a diffraction grating, the light beam is demultiplexed into aplurality of wavelength channels, each impinging on a corresponding MEMSswitch element 34. This MEMS can tilt both in the plane of thedispersion and in the plane perpendicular to the dispersion plane toroute the wavelength channels to alternate locations on the diffractiongrating 40. The images of these alternate locations through thetelescope can be made to precisely align to one of the micro-lens of thetwo dimensional array 32, thus each wavelength channel is made to coupleto a selectable optical port.

Throughout this description, a wavelength channel is an arbitrarycontiguous frequency band. A single wavelength channel might include oneor more ITU wavelengths and intervening wavelengths for example. Eventhough the expression “λ” is referred to herein in respect of awavelength channel, this is not intended to imply a wavelength channelis a single wavelength only.

By using a two dimensional arrangements of optical ports, the imageformed on the grating 40 containing all possible alternate locations issmall both in the dispersion plane and in the plane perpendicular to thedispersion plane. Compared to a prior art implementation as described inFIG. 1 expanded to include the same number of ports, the width of theimage in the plane of dispersion would be reduced by a factor of 6,which has a dramatic impact on optical performances of the system. Thelarger size of the embodiment as per the invention in the planeperpendicular to the dispersion plane has a small negative impact sincethe system remains mostly on-axis in that plane.

Therefore, assuming that 8 ports was the practical limitations imposedby optical design on an implementation as per the prior art, thetwo,dimensional arrangement of optical ports provided by the inventionwould enable building a device of up to 1×64 ports or with a smallernumber of ports but with improved optical performances and smaller size.These numerical values are for the purpose of explaining the improvementover the FIG. 1 arrangement. Other numbers of ports are possible.

FIG. 3 shows a perspective view. The two dimensional arrangement ofports and corresponding micro-lenses is clearly visible on this drawing.

FIG. 4 shows another embodiment as per co-application 50088-4 performinga similar function that the device shown on FIG. 3, but using waveguidebased dispersive elements.

This waveguide based dispersive element and the associated couplingoptics necessary to use it are described in applicants co-pendingapplications 60/381,364 filed on May 20, 2003 and <attorney docket50088-4> which is hereby incorporated by reference in its entirety.

FIG. 5 shows a wavelength cross-connect arrangement using free-spaceoptics and MEMS switching elements provided by an embodiment of theinvention. It basically consists of a first stack 54,56,58,60 and asecond stack 62,64,66,68 of dispersive arrangements connected togethervia optical paths established by MEMS micro-mirrors capable of tiltingin the plane perpendicular to the dispersion plane. More specifically,referring to the bottom view of FIG. 5, there are four input ports42,43,44,45 and four output ports 46,47,48,49. This designation betweeninput and output is arbitrary, and any port can function as either inputor output. Each input port 42,43,44,45 has a respective main lens80,82,84,86 through which light travels on the way to a respectivediffraction grating 62,64,66,68. Each diffraction grating 62,64,66,68redirects light back through the respective main lens 80,82,84,86 to arespective array of MEMS micro-mirrors 88,90,92,94. Each array of MEMSmicro-mirrors, for example array 88 shown in the top view, includes aseries of micro-mirrors arranged in a line perpendicular to the view inthe bottom of FIG. 5. Also shown is a second set of micro-mirror arrays96,98,100,102 each of which directs light through a respective main lens70,72,74,76 to a respective diffraction grating 54,56,58,60. Thediffraction gratings 54,56,58,60 redirect light back through the mainlens 70,72,74,76 and through output ports 46,47,48,49. The top view ofFIG. 5 shows functionality for input port 42 and output port 46. Eachport might include associated beam forming optics if necessary, thisbeing illustrated by the rectangles in the figure. This might forexample consist of being expanders/reducers, either spherical oranamorphic.

The arrangement of FIG. 5 allows any wavelength or combination ofwavelengths received on any input port to be routed to any of the outputports. It is noted that in this embodiment, the micro-mirrors in arrays88,90,92,94 only tilt in one plane. And as such light is alwaysreflected from one micro-mirror of one of the first arrays 88,90,92,94to a corresponding micro-mirror in one of the second arrays96,98,100,102. An example of this is shown in the top view of FIG. 5where input port functionality is shown in respect of the first inputport 42, and output port functionality is shown in respect of the firstoutput port 46. The route travelled by a single wavelength is indicatedgenerally at 108. A signal comes in through input port 42, and thispasses through the first port's main lens 80 to the first port'sdiffraction grating 62. This performs a wavelength dependent redirectionback through the main lens 80 to one of the micro-mirrors of the firstinput port's micro-mirror array 88. Specifically, light is directed ontomicro-mirror 104 forming part of micro-mirror array 88. In theillustrated example, it is assumed that this is the first micro-mirrorof array 88. This is reflected to a corresponding micro-mirror inmicro-mirror array 96, and in particular the first micro-mirror 106.Micro-mirror 106 reflects the light through the first output port's mainlens 70 to the first output port's diffraction grating 54 which performsa wavelength dependent redirection back through main lens 70 and throughthe output port 46.

In the example shown in FIG. 5, each stack contains four dispersivearrangements. One dispersive arrangement of each stack is shown in thetop view. The four dispersive arrangements are aligned on top of eachother as indicated in the figure. The two stacks are positioned one onthe left and one on the right hand side such that the MEMS mirrors fromthe first stack can establish an optical path to the MEMS mirrors in thesecond stack and vice-versa in at least the plane perpendicular to thedispersion plane.

In operation, four light beams containing a plurality of wavelengthchannels are input to the WXC on the four input ports 42,44,46,48(arbitrarily chosen as the left hand side top fibre stack in thefigure). The four light beams travel through their respective main lens80,82,84,86 to their respective diffraction grating 62,64,66,68 wherethey get demultiplexed into a respective plurality of wavelengthchannels. Each respective plurality of wavelength channels is routed toa corresponding first MEMS micro-mirror (one micro-mirror per input portand per wavelength channel) in the respective array 88,90,92,94 throughtheir respective main lens 80,82,84,86. These MEMS micro-mirrors canestablish an optical path to second MEMS micro-mirrors in arrays96,98,100,102 of the second stack of dispersive arrangements. Eachmicro-mirror of the arrays 96,98,100,102 is then tilted such that eachwavelength channel from each light beam is routed through theircorresponding second main lens 70,72,76,78 to their corresponding seconddiffraction grating 54,56,58,60 where they get remultiplexed into fourrespective light beams. These four respective light beams are routed tothe output optical ports 46,47,48,49 through their respective secondmain lens 70,72,74,76.

Another embodiment as per the invention but not shown uses transmissiveswitching means instead of MEMS micro-mirror arrays 88, 90, 92, 94, 96,98, 100, 102. The embodiment would look like the below described FIG. 11embodiment, but with only one part in the top view of FIG. 11, andmultiple parts in the bottom view.

In another embodiment, the embodiment of FIG. 5 is implemented usingwaveguide disperssive elements. The embodiment would look like theembodiment of FIG. 8 described below, but with only a single part oneach side in the top view, and multiple parts in the bottom view.

FIG. 6A shows an integrated WXC/ROADM device provided by an embodimentof the invention using free-space optics and MEMS switching elements, inwhich each ROADM has 5 local add/drop ports. This embodiment is similarto that of FIG. 5, but in this embodiment, to provide this addedfunctionality, the optical ports are now grouped in a first twodimensional array of ports 120 and a second two dimensional array ofports 122. More specifically, the input array of ports in theillustrated example consists of an array of four rows of five ports. The4×5 array of input ports 120 has an associated micro-lens 124 for eachinput port, and each column of ports has a respective collimating lens126. Similar coupling optics are provided at the output port 122. Theone dimensional tilting micro-mirror arrays 88,90,92,94,96,98,100,102 ofFIG. 5 are replaced with arrays 121,123,125,127,128,130,132,134 ofmicro-mirrors which are capable of tilting both in the plane ofdispersion and in the perpendicular plane to the dispersion plane. Forease of description of this figure, row refers to the dispersion plane,while column refers to the plane perpendicular to the dispersion plane.

In the plane perpendicular to the dispersion plane, the integratedWXC/ROADM looks similar to a simple WXC (like FIG. 5), with theexception of a slightly more complex coupling optics. In the dispersionplane, however, there are multiple optical ports provided per dispersivearrangement compared to only one in the embodiment of FIG. 5. Theseadded ports can be used for example as local add/drop ports, althoughother uses are possible without departing from the spirit of theinvention. Arbitrarily, the middle optical ports of each row of portsare chosen as an input/output ports, while the other ports are chosen asadd/drop ports.

In operation, four light beams containing a plurality of wavelengthchannels are input to the WXC on the four input ports of the input group(arbitrarily chosen as the left hand side top fibre stack in the sideview figure, middle column of the two dimensional array of opticalports). The four light beams are collimated by their respectivemicro-lenses corresponding to the middle column of the two dimensionalmicro-lens array and input to their respective dispersive arrangement.The four light beams travel through their respective main lens to theirrespective diffraction grating where they get demultiplexed into arespective plurality of wavelength channels. Each respective pluralityof wavelength channels is routed to a corresponding first MEMSmicro-mirror (one micro-mirror per input port and per wavelengthchannel) through their respective main lens. These MEMS micro-mirrorscan establish an optical path to second MEMS micro-mirrors of the secondstack of dispersive arrangements or send the light back towards theirrespective first dispersive arrangement.

For the beams being routed to these second MEMS elements, these secondMEMS micro-mirrors are tilted such that each wavelength channel fromeach light beam is routed through their corresponding second main lensto their corresponding second diffraction grating where they getremultiplexed into four respective light beams. These four respectivelight beams are routed to the output optical ports through theirrespective second main lens.

For the beams being routed back towards their respective firstdispersive arrangement, their corresponding first MEMS micro-mirror canbe tilted in the dispersion plane to route the corresponding wavelengthchannel to alternate locations on their respective diffraction grating.As explained in the description of FIG. 1, this alternate location isimaged to an alternate location in their respective micro-lens arrayrow, corresponding to a tuneable add/drop port.

Therefore, a function of simultaneously WXC (for the beams bouncing offfirst MEMS and second MEMS) and add/drop (for the beams bouncing offonly first MEMS) is provided in a single device.

FIG. 6B is a diagram showing the add/drop/switch functionality of theembodiment of FIG. 6A. For the embodiment of 6B, port 2000 is anarbitrary port from the left hand array of ports 120, and port 2006 isan arbitrary port from the right hand array of ports 122. Light is shownentering the port 2000. A wavelength channel dependent switchingfunction is realized as indicated generally at 2002. Through appropriateselection of the angle of the switching elements, any wavelength channelcan be returned to a port in the same row as input port 2000. Drop ports2008, 2010, 2012, 2014 are shown, functioning as the drop ports in thesame row as input port 2000. Any wavelength channel in the input signalcan be routed back to any of these drop ports. Similarly, any wavelengthchannel can be routed to a second switching element generally indicatedat 2004. Note the first switching element 2002 belongs to array 129while the second switching element 2004 belongs to array 128. A similarfunctionality is achieved at the output port 2006. Namely, any otherport in the same row as the output port 2006 can function as an addport. Ports 2016, 2018, 2020, 2022 are shown in the figure functioningas add ports. A wavelength channel can be input to any of these addports and will be added to the output signal at port 2006. Thus, withone bounce off the switching element, local drops at the input can beachieved and local drops at the output can be achieved with two bouncesoff the two sets of switching elements, a switching function from aninput port to any of the output ports is achieved.

In another embodiment the tilt in the dispersion plane is provided withthe second MEMS, not the first one, yielding different possibleapplication.

In yet another embodiment as per the invention, the tilt is provided byeither the first MEMS or the second MEMS depending on wavelengthchannels.

FIG. 7 shows a perspective view of the elements of the embodimentdescribed in FIG. 8 of an integrated WXC/ROADM using waveguide and MEMSconfigured as a 5×5 WXC wherein each optical port can have 5 localadd/drop paths (again counting the case of the light being directed fromthe input back to itself as a possible local add/drop path with the useof an external circulator).

FIG. 8 shows a preferred embodiment as per the invention in whichwaveguide dispersive elements are used in conjunction with MEMS basedarrays of switching means to realize an integrated ROADM/WXC device with5×5 wavelength cross-connect capacity and 1×5 local add/drop capabilityon each of the 5 incoming and 5 out coming ports.

This arrangement consists of a first two dimensional array of waveguidebased dispersive elements. These are realized through a stack of singledimensional arrays 200,204,206,208,210 each of which contains fivewaveguide dispersive elements. The waveguide dispersive elements290,292,294,296,298 of array 200 are shown in the perspective view ofFIG. 7. Each array 200,204,206,208,210 has a respective cylindrical lens212,214,216,218,220 to collimate/focus light beams emitted/received bythe waveguide dispersive elements in the plane perpendicular to thewaveguide substrate. Each waveguide device of the stack is furthercoupled to respective main cylindrical lens 222,224,226,228,230. Themain cylindrical lens is used to focus/collimate light beamsemitted/received by the waveguide dispersive element in the waveguidesubstrate's plane. The arrangement further comprises a first stack ofswitching elements 274 which is a two dimensional array of MEMSmicro-mirrors capable of tilting in two dimensions. Although MEMSmicro-mirrors are depicted in the figure, alternative switching elementscan also be used as mentioned previously. There is a second twodimensional array of micro-mirrors 272 which redirects light receivedfrom the first two dimensional array of micro-mirrors 274 through asecond set of main cylindrical lenses 232,234,236,238,240. There is asecond stack of arrays of waveguide dispersive elements260,262,264,268,270 with respective collimating lenses242,246,248,250,252 aligned with cylindrical lenses 232,234,236,238,240.

The different elements are arranged such that if a light beam containinga plurality of wavelength channels is input into one of the opticalports of the first stack of waveguide devices, it is dispersed by itsrespective waveguide dispersive elements into a plurality of light beamseach containing a wavelength channel. These light beams are routedthrough the respective cylindrical lens and main cylindrical lens to acorresponding switching element (there is one switching element perwavelength channel per waveguide device in a stack). These switchingelements can either send the light back towards their incoming waveguidedevice in the first stack, providing local add/drop ports or send thelight towards a corresponding second switching element of the secondstack of array of switching elements. These second switching elementscan route the beams towards any of the optical ports of thecorresponding waveguide device in the second stack.

Although in the figure there is provided a first array of maincylindrical lenses and a second array of main cylindrical lenses, it isapparent to a man skilled in the art that each of the lenses of thefirst and second array can be replaced by a single first and singlesecond bigger main cylindrical lenses. The embodiment featuring thebigger main cylindrical lenses is shown in the perspective view of FIG.7 whereas the embodiment showing arrays of main cylindrical lenses isshown in the views of FIG. 8.

FIG. 9 shows another embodiment of the invention of an integratedWXC/ROADM, in which the ROADM has a large number of ports based onMEMS+free space. This results from a two dimensional arrangement ofadd/drop ports for each of the dispersive arrangements. There is asimilar increase in number of add/drop ports going from the embodimentin FIG. 1 to the embodiment in FIG. 2 for a wavelength switch as goingfrom the embodiment in FIG. 6 to the embodiment in FIG. 9 for awavelength cross-connect.

The WXC/ROADM with large number of add/drop ports as per the inventionconsists of a first stack 900 and a second stack 902 of wavelengthswitch elements.

In what follows, only one element of each type of wavelength switchelement is labelled.

Each wavelength switch element comprises a two dimensional arrangementof optical ports 904 coupled through a first lens 906 and a main lens908 to a diffraction grating 910 and an array of switching elements 912.When a light beam containing a plurality of wavelength channels iscoupled to any of the optical ports, it is dispersed by the diffractiongrating into a plurality of optical beams each containing one wavelengthchannel. These optical beams are routed to a switching element of theswitching array. The wavelength switch is arranged such that there is afixed correspondence between the wavelength channel and the switchingelement for all possible optical ports. This is for example possiblewhen the diffraction grating and the array of switching elements liesubstantially in the focal planes of the main lens.

The two stacks of wavelength switch elements are arranged such that theswitching elements of the first stack of wavelength switches canestablish an optical path back to the corresponding wavelength switch ofthe first stack or to any other wavelength switch in the second stackand such that the switching elements of the second stack of wavelengthswitches can establish an optical path back to the correspondingwavelength switch of the second stack or to any other wavelength switchin the first stack.

In operation, a plurality of optical paths can be established throughthe WXC/ROADM device in which light can be routed from any optical portsof any of the wavelength switch from the first stack to any of theoptical ports of the corresponding wavelength switch for local add/dropor routed to any of the optical ports of any of the wavelength switchesfrom the second stack.

In the Figure, an example path is shown going from the middle port (3rdrow and 3rd column) of the first of the left group of 2D arrangements ofports to the fourth row and fifth column of the first of the left groupof the 2D arrangement of ports (black line turning into light grey line)and another example path is shown from the middle ports of the first ofthe left group of 2D arrangements of ports to the middle port of thethird of the right group of 2D arrangement of ports.

FIG. 10 shows a WG embodiment of the invention shown in FIG. 9 toprovide an integrated WXC/ROADM with a large number of add/drop ports.This embodiment is similar to that of FIG. 9 with the ports anddiffraction gratings replaced with waveguide dispersive elements.

The device consists of a first group 1000 and a second group 1002 ofstacks of waveguide devices. Each waveguide device comprises an array ofat least one waveguide based dispersive element. For each stack ofwaveguide device e.g. stack 1004, there is provided an array ofswitching elements 1010. For each waveguide device in each stack e.g.device 1006 of stack 1004, there is a corresponding cylindrical lens1008 to collimate/focus light beams emitted/received from the waveguidedevice in the plane of the waveguide substrate and to create an opticalpath from the waveguide device to the array of switching elementscorresponding to their stack. For each waveguide device, there isfurther provided a corresponding main cylindrical lens 1020 tofocus/collimate light beams emitted/received from the waveguide devicein the dispersion plane. These main cylindrical lenses can be replacedby a single bigger main cylindrical lens for each waveguide device orfor each stack.

The first switching elements 1010 are arranged such that an optical pathcan be established from any of the optical ports of any waveguide deviceof any stacks of the first group 1000 to either any of the optical portsof any waveguide device in the same stack of the first group 1000 or toany of the optical ports of any waveguide device of any stacks of thesecond group 1002. The second switching elements 1012 are arranged suchthat an optical path can be established from any of the optical ports ofany waveguide device of any stacks of the second group 1002 to eitherany of the optical ports of any waveguide device in the same stack ofthe second group 1002 or to any of the optical ports of any waveguidedevice of any stacks of the first group 1000.

FIG. 11 shows an alternate embodiment as per the invention similar infunctionality and mode of operation to FIG. 6 in which the first 1100and second array 1102 of switching means are transmissive beam steeringelements.

FIG. 12 shows an alternate embodiment as per the invention similar infunctionality and mode of operation to FIG. 8 in which the first 1200and second array 1202 of switching means are transmissive beam steeringelements.

The embodiments featuring waveguide dispersive elements are shown toinclude integrated port coupling optics. Alternatively, the couplingoptics can be realized with separate micro-optics coupling schemes.

The invention is not intended to be limited to the above mentionedspecific embodiments but should rather be understood as being within thescope of the appended claims.

1. A wavelength cross connect comprising: a first plurality of lensesstacked vertically; a second plurality of lenses stacked vertically,spaced from said first plurality of lenses, non-overlapping in verticalspace with said first plurality of lenses; a first plurality ofdispersive elements, with one dispersive element substantially in afirst focal plane of each of said first plurality of lenses; a secondplurality of dispersive elements, with one dispersive elementsubstantially in a second focal plane of each of said second pluralityof lenses; a first array of switching elements controllable in twodirections, the first array being substantially in a second focal planeof each of said first plurality of lenses; a second array of switchingelements controllable in two directions, the second array beingsubstantially in a first focal plane of each of said second plurality oflenses; in a first plurality of optical ports a respective optical portpositioned to input light onto/receive light from each of said firstplurality of lenses; in a second plurality of optical ports a respectiveoptical port positioned to input light onto/receive light from each ofsaid second plurality of lenses; wherein light entering any of saidfirst plurality of optical ports or said second plurality of ports isswitchable to any of the first plurality of optical ports and any ofsaid second plurality of optical ports.
 2. A wavelength cross connectaccording to claim 1 wherein the switching elements are MEMS switchingelements.
 3. A wavelength cross connect according to claim 1 whereineach first bulk optical element is selected from a group consisting of alens or a curved mirror.
 4. A wavelength cross connect according toclaim 1 wherein the dispersive element is selected from a groupconsisting of: a diffraction grating, either reflection and transmissiontype, prisms.
 5. A wavelength cross connect comprising: a firstplurality of lenses stacked vertically; a second plurality of lensesstacked vertically, spaced from said first plurality of lenses,non-overlapping in vertical space with said first plurality of lenses; afirst dispersive element at least part of which is substantially in afirst focal plane of each of said first plurality of lenses; a seconddispersive element at least part of which is substantially in a secondfocal plane of each of said second plurality of lenses; a first array ofswitching elements controllable in two directions, the first array beingsubstantially in a second focal plane of each of said first plurality oflenses; a second array of switching elements controllable in twodirections, the second array being substantially in a first focal planeof each of said second plurality of lenses; in a first plurality ofoptical ports a respective optical port positioned to input lightonto/receive light from each of said first plurality of lenses; in asecond plurality of optical ports a respective optical port positionedto input light onto/receive light from each of said second plurality oflenses; wherein light entering any of said first plurality of opticalports or said second plurality of ports is switchable to any of thefirst plurality of optical ports and any of said second plurality ofoptical ports.
 6. A wavelength cross connect according to claim 5wherein the switching elements are MEMS switching elements.
 7. Awavelength cross connect according to claim 5 wherein each first bulkoptical element is selected from a group consisting of a lens or acurved mirror.
 8. A wavelength cross connect according to claim 5wherein the dispersive element is selected from a group consisting of: adiffraction grating, either reflection and transmission type, prisms. 9.A wavelength cross connect comprising: a first plurality of lensesstacked vertically; a second plurality of lenses stacked vertically,spaced from said first plurality of lenses, non-overlapping in verticalspace with said first plurality of lenses; a first plurality ofdispersive elements, with one dispersive element substantially in afirst focal plane of each of said first plurality of lenses; a secondplurality of dispersive elements, with one dispersive elementsubstantially in a second focal plane of each of said second pluralityof lenses; a first array of transmissive switching elements controllablein two directions, the first array being substantially in a second focalplane of each of said first plurality of lenses; a second array oftransmissive switching elements controllable in two directions, thesecond array being substantially in a first focal plane of each of saidsecond plurality of lenses; in a first plurality of optical ports arespective optical port positioned to input light onto/receive lightfrom each of said first plurality of lenses; in a second plurality ofoptical ports a respective optical port positioned to input lightonto/receive light from each of said second plurality of lenses; whereinlight entering any of said first plurality of optical ports or saidsecond plurality of ports is switchable to any of the first plurality ofoptical ports and any of said second plurality of optical ports.
 10. Awavelength cross connect according to claim 9 wherein the transmissiveswitching elements are one of a liquid crystal beam steering element, anacousto-optic beam deflector, part of a solid state phase array, acontrollable hologram, a periodically poled Lithium Niobate beamdeflector.
 11. A wavelength cross connect according to claim 9 whereineach first bulk optical element is selected from a group consisting of alens or a curved mirror.
 12. A wavelength cross connect according toclaim 9 wherein the dispersive element is selected from a groupconsisting of: a diffraction grating, either reflection and transmissiontype, prisms.
 13. A wavelength cross connect comprising: a firstplurality of lenses stacked vertically; a second plurality of lensesstacked vertically, spaced from said first plurality of lenses,non-overlapping in vertical space with said first plurality of lenses; afirst plurality of dispersive elements, with one dispersive elementsubstantially in a first focal plane of each of said first plurality oflenses; a second plurality of dispersive elements, with one dispersiveelement substantially in a second focal plane of each of said secondplurality of lenses; a first array of switching elements controllable intwo directions, the first array being substantially in a second focalplane of each of said first plurality of lenses; a second array ofswitching elements controllable in two directions, the second arraybeing substantially in a first focal plane of each of said secondplurality of lenses; a first two dimensional array of optical ports; asecond two dimensional array of optical ports; for each row of saidfirst two dimensional array of optical ports, a respective first bulkoptical element having optical power and having a fourth focal planesubstantially coplanar with said first focal plane of said secondplurality of lenses; for each row of said second two dimensional arrayof optical ports, a respective second bulk optical element havingoptical power and having a fifth focal plane substantially coplanar withsaid second focal plane of said first plurality of lenses; wherein eachwavelength channel of a WDM signal entering at a port of said firstarray of optical ports is individually switchable to any of the port infirst array of optical ports in a same row as the port where the WDMsignal entered and any of the second array of optical ports throughappropriate control of the array of switching elements.
 14. A wavelengthcross connect according to claim 13 wherein the switching elements areMEMS switching elements.
 15. A wavelength cross connect according toclaim 13 wherein each bulk optical element is a lens or a curved mirror.16. A wavelength cross connect according to claim 13 wherein thedispersive element is selected from a group comprising: a diffractiongrating, either reflection and transmission type, prisms.
 17. Awavelength cross connect comprising: a first plurality of lenses stackedvertically; a second plurality of lenses stacked vertically, spaced fromsaid first plurality of lenses, non-overlapping in vertical space withsaid first plurality of lenses; a first plurality of dispersiveelements, with one dispersive element substantially in a first focalplane of each of said first plurality of lenses; a second plurality ofdispersive elements, with one dispersive element substantially in asecond focal plane of each of said second plurality of lenses; a firstarray of switching elements controllable in two directions, the firstarray being substantially in a second focal plane of each of said firstplurality of lenses; a second array of switching elements controllablein two directions, the second array being substantially in a first focalplane of each of said second plurality of lenses; a first twodimensional array of optical ports; a second two dimensional array ofoptical ports; a first bulk optical element having optical power andhaving a fourth focal plane substantially coplanar with said first focalplane of said second plurality of lenses; a second optical elementhaving optical power and having a fifth focal plane substantiallycoplanar with said second focal plane of said first plurality of lenses;wherein each wavelength channel of a WDM signal entering at a port ofsaid first array of optical ports is individually switchable to any ofthe port in first array of optical ports in a same row as the port wherethe WDM signal entered and any of the second array of optical portsthrough appropriate control of the array of switching elements.
 18. Awavelength cross connect according to claim 17 wherein the switchingelements are MEMS switching elements.
 19. A wavelength cross connectaccording to claim 17 wherein each bulk optical element is a lens or acurved mirror.
 20. A wavelength cross connect according to claim 17wherein the dispersive element is selected from a group comprising: adiffraction grating, either reflection and transmission type, prisms.21. An arrangement comprising: a first two dimensional array of opticalports; a first two dimensional array of waveguide dispersive elements ona plurality of waveguide substrates, with one waveguide dispersiveelement per optical port in said first two dimensional array of opticalports, the first two dimensional array of waveguide dispersive elementscollectively having a first output plane; for each row of said first twodimensional array of optical ports, a respective first bulk opticalelement having optical power and having a first focal planesubstantially coplanar with said first output plane, and having a secondfocal plane; a first array of switching elements substantially in thesecond focal plane, each switching element being adapted to switch inboth a horizontal and vertical direction; a second two dimensional arrayof optical ports; a second two dimensional array of waveguide dispersiveelements on a plurality of waveguide substrates, with one waveguidedispersive element per optical port in said second two dimensional arrayof optical ports, the second two dimensional array of waveguidedispersive elements collectively having a second output plane; for eachrow of said second two dimensional array of optical ports, a respectivesecond bulk optical element having optical power and having a fifthfocal plane and having a sixth focal plane substantially coplanar withthe second output plane; a second array of switching elementssubstantially in the fifth focal plane, each switching element beingadapted to switch in both a horizontal and vertical direction; whereineach wavelength channel of a WDM signal entering at one of said firstarray of optical ports is individually switchable to any of the opticalports of the first array in a same row as the port through which thesignal entered and any of the optical ports of the second array throughappropriate control of the array of switching elements.
 22. Anarrangement according to claim 21 wherein the switching elements areMEMS switching elements.
 23. An arrangement according to claim 21wherein each bulk optical element having optical power is a lens or acurved mirror.
 24. An arrangement according to claim 21 wherein thedispersive elements comprise arrayed waveguide gratings or Echellegratings.
 25. An arrangement comprising: a first two dimensional arrayof optical ports; a first two dimensional array of waveguide dispersiveelements on a plurality of waveguide substrates, with one waveguidedispersive element per optical port in said first two dimensional arrayof optical ports, the first two dimensional array of waveguidedispersive elements collectively having a first output plane; a firstbulk optical element having optical power and having a first focal planesubstantially coplanar with said first output plane, and having a secondfocal plane; a first array of switching elements substantially in thesecond focal plane, each switching element being adapted to switch inboth a horizontal and vertical direction; a second two dimensional arrayof optical ports; a second two dimensional array of waveguide dispersiveelements on a plurality of waveguide substrates, with one waveguidedispersive element per optical port in said second two dimensional arrayof optical ports, the second two dimensional array of waveguidedispersive elements collectively having a second output plane; a secondbulk optical element having optical power and having a fifth focal planesubstantially coplanar with the second output plane; a second array ofswitching elements substantially in the fifth focal plane, eachswitching element being adapted to switch in both a horizontal andvertical direction; wherein each wavelength channel of a WDM signalentering at one of said first array of optical ports is individuallyswitchable to any of the optical ports of the first array in a same rowas the port through which the signal entered and any of the opticalports of the second array through appropriate control of the array ofswitching elements.
 26. An arrangement according to claim 25 wherein theswitching elements are MEMS switching elements.
 27. An arrangementaccording to claim 25 wherein each bulk optical element having opticalpower is a lens or a curved mirror.
 28. An arrangement according toclaim 25 wherein the dispersive elements comprise arrayed waveguidegratings or Echelle gratings.
 29. A wavelength cross connect comprising:a first plurality of lenses stacked vertically; a second plurality oflenses stacked vertically, spaced from said first plurality of lenses,non-overlapping in vertical space with said first plurality of lenses; afirst plurality of dispersive elements, with one dispersive elementsubstantially in a first focal plane of each of said first plurality oflenses; a second plurality of dispersive elements, with one dispersiveelement substantially in a second focal plane of each of said secondplurality of lenses; a first array of transmissive switching elementscontrollable in two directions, the first array being substantially in asecond focal plane of each of said first plurality of lenses; a secondarray of transmissive switching elements controllable in two directions,the second array being substantially in a first focal plane of each ofsaid second plurality of lenses; a first two dimensional array ofoptical ports; a second two dimensional array of optical ports; for eachrow of said first two dimensional array of optical ports, a respectivefirst bulk optical element having optical power and having a fourthfocal plane substantially coplanar with said first focal plane of saidsecond plurality of lenses; for each row of said second two dimensionalarray of optical ports, a respective second bulk optical element havingoptical power and having a fifth focal plane substantially coplanar withsaid second focal plane of said first plurality of lenses; wherein eachwavelength channel of a WDM signal entering at port of said first arrayof optical ports is individually switchable to any of the port in firstarray of optical ports in a same row as the port where the WDM signalentered and any of the second array of optical ports through appropriatecontrol of the array of switching elements.
 30. A wavelength crossconnect according to claim 29 wherein each bulk optical element a lensor a curved mirror.
 31. A wavelength cross connect according to claim 29wherein the dispersive element is selected from a group comprising: adiffraction grating, either reflection and transmission type, prisms.32. A wavelength cross connect comprising: a first plurality of lensesstacked vertically; a second plurality of lenses stacked vertically,spaced from said first plurality of lenses, non-overlapping in verticalspace with said first plurality of lenses; a first plurality ofdispersive elements, with one dispersive element substantially in afirst focal plane of each of said first plurality of lenses; a secondplurality of dispersive elements, with one dispersive elementsubstantially in a second focal plane of each of said second pluralityof lenses; a first array of transmissive switching elements controllablein two directions, the first array being substantially in a second focalplane of each of said first plurality of lenses; a second array oftransmissive switching elements controllable in two directions, thesecond array being substantially in a first focal plane of each of saidsecond plurality of lenses; a first two dimensional array of opticalports; a second two dimensional array of optical ports; a first bulkoptical element having optical power and having a fourth focal planesubstantially coplanar with said first focal plane of said secondplurality of lenses; a second optical element having optical power andhaving a fifth focal plane substantially coplanar with said second focalplane of said first plurality of lenses; wherein each wavelength channelof a WDM signal entering at port of said first array of optical ports isindividually switchable to any of the port in first array of opticalports in a same row as the port where the WDM signal entered and any ofthe second array of optical ports through appropriate control of thearray of switching elements.
 33. A wavelength cross connect according toclaim 32 wherein each bulk optical element a lens or a curved mirror.34. A wavelength cross connect according to claim 32 wherein thedispersive element is selected from a group comprising: a diffractiongrating, either reflection and transmission type, prisms.
 35. Anarrangement comprising: a first plurality of lenses stacked vertically;a second plurality of lenses stacked vertically, spaced from said firstplurality of lenses, non-overlapping in vertical space with said firstplurality of lenses; a first plurality of dispersive elements, with onedispersive element substantially in a first focal plane of each of saidfirst plurality of lenses; a second plurality of dispersive elements,with one dispersive element substantially in a second focal plane ofeach of said second plurality of lenses; a first array of switchingelements controllable in two directions, the first array beingsubstantially in a second focal plane of each of said first plurality oflenses; a second array of switching elements controllable in twodirections, the second array being substantially in a first focal planeof each of said second plurality of lenses; a first plurality of twodimensional arrays of optical ports; a second plurality of twodimensional arrays of optical ports; for each two dimensional array ofsaid first plurality of two dimensional arrays of optical ports, arespective first bulk optical element having optical power and having afourth focal plane substantially coplanar with said first focal plane ofsaid second plurality of lenses; for each two dimensional array of saidsecond plurality of two dimensional arrays of optical ports, arespective second bulk optical element having optical power and having afifth focal plane substantially coplanar with said second focal plane ofsaid first plurality of lenses; wherein each wavelength channel of a WDMsignal entering at one of said first plurality of arrays of opticalports is individually switchable to any of the first plurality of arraysof optical ports and any of the second plurality of arrays of opticalports through appropriate control of the array of switching elements.36. An arrangement according to claim 35 wherein the switching elementsare MEMS switching elements.
 37. An arrangement according to claim 35wherein the switching elements are transmissive.
 38. An arrangementaccording to claim 35 wherein each bulk optical element is selected froma group consisting of a lens, a curved mirror, an assembly of lenses andmirrors, and an assembly of lenses, mirrors and a curved mirror.
 39. Anarrangement according to claim 35 wherein the second bulk opticalelement is selected from a group consisting of a lens, a curved mirror,an assembly of lenses and mirrors, and an assembly of lenses, mirrorsand a curved mirror.
 40. An arrangement according to claim 35 whereinthe dispersive element is selected from a group comprising: adiffraction grating, either reflection and transmission type, prisms.